1. Field of the Invention
The invention relates to organopolysiloxane/polyurea/polyurethane block copolymers.
2. Description of the Related Art
The properties of polyurethanes and silicone elastomers are complementary in many areas. Polyurethanes are notable for their outstanding mechanical strength, elasticity, and very good adhesion, abrasion resistance, and ease of processing by extrusion from the melt. Silicone elastomers, on the other hand, possess an excellent temperature, UV stability, and weathering stability. They retain their elastic properties at relatively low temperatures and consequently do not tend toward embrittlement either. In addition they possess special water repellency and antistick surface properties.
Conventional polysiloxanes are employed for elastomers, seals, adhesives, and sealants or antistick coatings in the form of thixotropic pastes. In order to achieve the desired ultimate strengths different ways of curing the compositions have been developed, with the objective of fixing the desired structures and setting the mechanical properties. In the majority of cases, however, the polymers must be blended, by the addition of reinforcing additives, such as pyrogenic silicas, for example, in order to attain adequate mechanical properties. In the curing systems a distinction is made essentially between high temperature vulcanizing (HTV) systems and room temperature vulcanizing (RTV) systems. In the case of the RTV compositions there are both one-component (1K) and two-component (2K) systems. In the 2K systems, the two components are mixed and hence catalytically activated and cured. The curing mechanism and the catalyst required can in this case be different. Curing is normally accomplished by peroxidic crosslinking, by hydrosilylation by means of platinum catalysis or, for example, by condensation reactions. Although such 2K systems possess very long pot lives, the attainment of optimum properties requires very precise compliance with the mixing proportions of the two components, leading to increased complexity of apparatus in processing. 1K systems likewise cure by peroxidic crosslinking, by hydrosilylation by means of platinum catalysis or, for example, by condensation reactions. In this case, however, either an additional processing step for compounding in the crosslinking catalyst is necessary or the compositions have only a limited pot life. A feature common to all these systems, however, is that the products are insoluble after processing and also, for example, can no longer be recycled.
Consequently the combination of urethane polymers and silicone polymers ought to provide access to materials having good mechanical properties, which at the same time feature processing possibilities which are greatly simplified as compared with the silicones, while continuing to possess the positive properties of the silicones. The combination of the advantages of both systems can therefore lead to compounds having low glass transition temperatures, low surface energies, improved thermal and photochemical stabilities, low water absorption, and physiologically inert materials.